An open, prospective and randomized study was carried on which compared two isocaloric energy intakes. We tried to demonstrate that fructose-glucose-xylitol mixture (FGX) is better tolerated than glucose in two groups of patients with systemic inflammatory response syndrome (SIRS). In one of them patients were suffering acute pneumonia with sepsis, and the other necro-hemorrhagic pancreatitis. Exclusion criteria were: diabetes, previous hypertriglyceridemia, renal failure with serum creatinine > 3m/dL at admittance in ICU, or hyperbilirrubinemia > 2.5 mg/dL. Total parenteral nutrition (TPN), consisting in 1.4 g AA + 35 kcal/kg (Lipids 1.5 + carbohydrates 4 g/kg/d, either glucose or FGX at random) was administered. Basal levels and days 1st, 4th, and 10th plasma measurements of glucose, triglycerides and cholesterol were determined. Insulin was given if glycemia rose above 180 mg/dL. During 48 months, 119 patients who were admitted at the ICU, 72 with pneumonia and 47 with pancreatitis, were included. Tolerance was similar with both nutrients in pneumonia patients. Glycemia was kept at the same level with both energetic intakes, but the amount of insulin given was significantly more in those patients fed on glucose (p<0.05). On the other hand, resting blood glucose and triglyceride levels were higher in pancreatitic patients, and more insulin was required. Those on FGX had lower triglyceride plasma levels (p<0.05) and less insulin was given throughout the study. Glycemia was kept lower though no statistical significance was reached (p<0.1).